Fertilizer technology is as old as human civilization and often utilizes fecal matter from animal husbandry. However, due to greater understanding of plant physiology, empirical results leading to improved practices, and better equipment, this field continuously advances.
A very interesting discovery has been that calcium added as a plant nutrient benefits postharvest storage, via a change in physiology of many plants such as pome fruit, potatoes and some green vegetables. See for example “The Role of Calcium and Nitrogen in Postharvest Quality and Disease Resistance of Apples” (Fallahi et al, HortScience, Vol. 32(5), August 1997). As a result, some basic science has focused on direct calcium feeding by adding a readily absorbable source such as calcium chloride and calcium nitrate as exemplified by Cihacek et al from North Dakota State University “Effects of Calcium and Nitrogen Fertilizer Application on Carrot Root Yield and Storage Quality” (www.ag.ndsu.nodak.edu/oakes/1999Report/crfrt99.htm).
Companies involved in mineral extraction, use and recycling have discovered that minerals such as lime and gypsum can be used as soil supplements, primarily to improve the physical characteristics of the soil.
For example, USA Gypsum exhorts the advantages of Gypsum added and directly mixed into soil to prevent soil compaction (www.usagypsum.conm/agricultural-gypsum.aspx).
One problem of fertilizer application is how to apply (high energy to mixing into the soil vs. lower energy scatter on top of soil, spray onto leaves, etc. Another is the occasional need for slow, long term release, to prevent wastage via quick runoff of high soluble plant nutrients. Accordingly, any form of fertilizer that provides a more convenient application method, or control of dissolution, would be an important tool in the farmer's arsenal for controllable delivery of plant nutrients such as calcium and sulfur, where and when needed. In some cases, application of a mineral such as gypsum requires an expensive screening step and use of a non-nutritive or expensive binder such as clay, lignin or starch as, for example, described by Steele et al in U.S. No. 2001/0029762A1 “Soil Amendment Product and Process.” In contrast, it would be most desirable to both control dissolution of soluble minerals via packaging of the mineral with a desirable fertilizer component. Such low cost, controlled solution also would benefit the farmer.